In the production of flexible tubular members, such as food casings and the like, it is frequently desirable to coat and/or layer the interior surface of the tubular member with one or more of various compositions to achieve various effects. For example, when the tubular member is a cellulosic food casing, it may be desirable to coat the interior surface thereof with a moisture proof barrier coating containing compounds such as polyvinylidene chloride, polyolefins, vinyls, polyesters, nylons or other suitable copolymers and polymers; to coat the interior of the casing with compositions containing food release additives, or lubricants; to coat the interior of the casing with compositions containing a colorant or flavorant composition; or, any of multiple other compositions.
U.S. Pat. No. 3,378,379, describes one method of internally coating flexible tubular members wherein the coating composition is applied in a "slugg" to the interior of the tube during processing. Disadvantages of such process are the difficulty of controlling quality, quantity and drying the coating applied. One solution to the problems associated with slugg coating methods has been to coat the external surfaces of the tubular member, under regulated conditions to obtain the desired quantity and quality of coating being applied, then turning the tubing inside out so as to position the controlled coated surface on the interior of the tubing, a process called "everting".
U.S. Pat. No. 3,242,524 describes a method of everting wherein a substantially air impermeable tubular material having a closed end is everted by utilizing a pressure differential to pull the closed end portion through the noneverted casing. Such everting method requires a great deal of space and energy to achieve its goal and is only operable with substantially air impermeable tubular material having sufficient circumferential or hoop strength to resist the imposed air pressure.
U.S. Pat. No. 4,073,737 describes a device for everting tubular casing wherein the casing is passed through a ring member, folded back over the exterior surface of the casing and the ring member is displaced relative to the fixed casing end thereby everting the casing. The ring member is electromagnetically coupled to the displacing apparatus to obtain displacement. Such process requires substantial tensile strength of the casing in that it must be strong enough to sustain the forces necessary to "pull" itself through the point of everting plus withstand the weight of its unsupported length. There is also an incremental increase of abrasion at the point of everting which results from the electromagnetic attachment of the displacing apparatus and the ring member.
U.S. Pat. No. 4,162,557 describes a method and device of everting wherein tubular casing is shirred on a "stick", the end of the casing is closed and the tubing everted during deshirring by pulling one end of the shirred tubing through the bore of the shirred stick and out through the opposite end.
U.S. Pat. No. 4,292,711 describes a similar process and device for everting a shirred stick wherein the everting process is achieved during deshirring and stuffing of the casing with emulsified food products, thus pulling the casing through the opposite end utilizing the stuffing pressure differential. It should be readily apparent that coupling the everting process with shirring and/or stuffing significantly limits the commercial use of the process.
It is, therefore, a primary object of the present invention to provide a device for everting flexible tubular members which overcome the shortcomings of the prior art.
It is a further object to provide an everting method which permits space and energy efficient everting of unshirred flexible tubular members.
It is a still further object of the present invention to provide an everting method and device which acts to reduce the pulling forces at the point of everting.
These and other objects of the invention will become apparent from the specification, claims and the accompanying drawings.